V.A.J.M. Sleiffer

73.7 Tb/s (96 x 3 x 256-Gb/s) mode-division-multiplexed DP-16QAM transmission with inline MM-EDFA

Transmission of a 73.7 Tb/s (96 x 3 x 256-Gb/s) DP-16QAM mode-division-multiplexed signal over 119 km of few-mode fiber transmission line incorporating an inline multi mode EDFA and a phase plate based mode (de-)multiplexer is demonstrated. Data-aided 6 x 6 MIMO digital signal processing was used to demodulate the signal. The total demonstrated net capacity, taking into account 20% of FEC-overhead and 7.5% additional overhead (Ethernet and training sequences), is 57.6 Tb/s, corresponding to a spectral efficiency of 12 bits/s/Hz.

DSP complexity of mode-division multiplexed receivers

The complexities of common equalizer schemes are analytically analyzed in this paper in terms of complex multiplications per bit. Based on this approach we compare the complexity of mode-division multiplexed digital signal processing algorithms with different numbers of multiplexed modes in terms of modal dispersion and distance. It is found that training symbol based equalizers have significantly lower complexity compared to blind approaches for long-haul transmission. Among the training symbol based schemes, OFDM requires the lowest complexity for crosstalk compensation in a mode-division multiplexed receiver. The main challenge for training symbol based schemes is the additional overhead required to compensate modal crosstalk, which increases the data rate. In order to achieve 2000 km transmission, the effective modal dispersion must therefore be below 6 ps/km when the OFDM specific overhead is limited to 10%. It is concluded that for few mode transmission systems the reduction of modal delay is crucial to enable long-haul performance.

Reduced Complexity Digital Back-Propagation Methods for Optical Communication Systems

Next-generation optical communication systems will continue to push the ( bandwidth · distance) product towards its physical limit. To address this enormous demand, the usage of digital signal processing together with advanced modulation formats and coherent detection has been proposed to enable data-rates as high as 400 Gb/s per channel over distances in the order of 1000 km. These technological breakthroughs have been made possible by full compensation of linear fiber impairments using digital equalization algorithms. While linear equalization techniques have already matured over the last decade, the next logical focus is to explore solutions enabling the mitigation of the Kerr effect induced nonlinear channel impairments. One of the most promising methods to compensate for fiber nonlinearities is digital back-propagation (DBP), which has recently been acknowledged as a universal compensator for fiber propagation impairments, albeit with high computational requirements. In this paper, we discuss two proposals to reduce the hardware complexity required by DBP. The first confirms and extends published results for non-dispersion managed link, while the second introduces a novel method applicable to dispersion managed links, showing complexity reductions in the order of 50% and up to 85%, respectively. The proposed techniques are validated by comparing results obtained through post-processing of simulated and experimental data, employing single channel and WDM configurations, with advanced modulation formats, such as quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16-QAM). The considered net symbol rate for all cases is 25 GSymbol/s. Our post-processing results show that we can significantly reduce the hardware complexity without affecting the system performance. Finally, a detailed analysis of the obtained reduction is presented for the case of dispersion managed link in terms of number of required complex multiplications per transmitted bit.

High Capacity Mode-Division Multiplexed Optical Transmission in a Novel 37-cell Hollow-Core Photonic Bandgap Fiber

We present the first demonstration of combined wavelength-division multiplexed (WDM) and mode-division multiplexed (MDM) optical transmission in a hollow-core photonic bandgap fiber (HC-PBGF). For this purpose a novel low loss, broadband 310 m long HC-PBGF with a 37 cell (37c) core geometry is used. The modal properties of the HC-PBGF are characterized in detail, showing an absence of surface modes and low modal crosstalk, which enable WDM and MDM transmission with record high capacity (73.7 Tb/s) for a HC-PBGF. Several modulation formats have been tested, showing very good and stable performance. The transmission properties are assessed by looking into both single-mode transmission and MDM transmission, showing good agreement with the modal characterization of the 37c HC-PGBF.

20 × 960-Gb/s Space-division-multiplexed 32QAM transmission over 60 km few-mode fiber

We show transmission of 20 wavelength-division-multiplexed (WDM) × 960-Gb/s space-division-multiplexed 32QAM modulated channels (spectral efficiency (SE) of 15 bits/s/Hz) over 60 km of few-mode fiber (FMF) with inline few-mode EDFA (FM-EDFA). Soft-decision FEC was implemented and used to achieve error-free transmission.

Three mode Er3+ ring-doped fiber amplifier for mode-division multiplexed transmission

We successfully fabricate three-mode erbium doped fiber with a confined Er(3+) doped ring structure and experimentally characterize the amplifier performance with a view to mode-division multiplexed (MDM) transmission. The differential modal gain was effectively mitigated by controlling the relative thickness of the ring-doped layer in the active fiber and pump launch conditions. A detailed study of the modal gain properties, amplifier performance in a MDM transmission system and inter-modal cross-gain modulation and associated transient effects is presented.

MIMO equalization with adaptive step size for few-mode fiber transmission systems

Optical multiple-input multiple-output (MIMO) transmission systems generally employ minimum mean squared error time or frequency domain equalizers. Using an experimental 3-mode dual polarization coherent transmission setup, we show that the convergence time of the MMSE time domain equalizer (TDE) and frequency domain equalizer (FDE) can be reduced by approximately 50% and 30%, respectively. The criterion used to estimate the system convergence time is the time it takes for the MIMO equalizer to reach an average output error which is within a margin of 5% of the average output error after 50,000 symbols. The convergence reduction difference between the TDE and FDE is attributed to the limited maximum step size for stable convergence of the frequency domain equalizer. The adaptive step size requires a small overhead in the form of a lookup table. It is highlighted that the convergence time reduction is achieved without sacrificing optical signal-to-noise ratio performance.

Transmission of 448-Gb/s dual-carrier POLMUX-16QAM over 1230 km with 5 flexi-grid ROADM passes

We show the compatibility of 448-Gb/s dual-carrier POLMUX-16QAM modulation with a 87.5-GHz flexi-grid channel spacing in the presence of cascaded optical filtering, enabling transmission over 1230 km and 5 ROADM passes with 4.8-b/s/Hz spectral efficiency.

First demonstration of a broadband 37-cell hollow core photonic bandgap fiber and its application to high capacity mode division multiplexing

We report fabrication of the first low-loss, broadband 37-cell photonic bandgap fiber. Exploiting absence of surface modes and low cross-talk in the fiber we demonstrate mode division multiplexing over three modes with record transmission capacity.

Demonstration of a Photonic Integrated Mode Coupler With MDM and WDM Transmission

In this letter, 3.072-Tb/s (six spatial and polarization modes × 4 wavelength-division multiplexing (WDM) ×128-Gb/s 16QAM) transmission over 30 km of few-mode fiber (FMF) is demonstrated employing a photonic integrated mode coupler based on silicon-on-insulator (SoI) technology. A 2-D top coupling solution with five small vertical grating couplers is proposed for coupling between an SoI chip and an FMF, guiding LP01 and LP11 modes. Push-pull and center launch configurations for exciting LP11 and LP01 modes, respectively, through mode-profile matching are analyzed and implemented on the SoI chip.